[9S08SH] How to have a robust power on reset (POR)?

[ecb]

Hi all,

I use 9S08SH4 (TSSOP16) at 3.3 V but it does not start after a power on following immediately a power off. In this case, I just have to touch any component on my PCB so that it starts. If I wait for a few seconds before the power on it starts normally. I use two regulations of tension, linear regulator and buck converter but this issue appears in both cases.

An idea please?

[Paul_Tian]

Hi, Ecb

MC9S08 series product has a power on timing requirement. You need to follow it. So I suggest you add a capacitor on your VDD pin. The value can be 10uF.

Hope my reply can help you. Thanks.

Best Regards

Paul

[ecb]

Hi Paul and thanks for the answer.

I will try your solution but I do not think that the problem comes from the power supply. The output filter include 22µF close to the switching regulator + 1500µF + 0.1µF close to all the devices and I have less of 10mV of ripple.

I tried a R/C cell on the reset pin without result. I will try also a reset supervisor with timer.

Best regards

Claude